Thanks Interceptor121 & makar0n for the tips. My AA batteries are on the charger now and I will run some experiments tomorrow to see if I can resolve it. I only use the strobes in manual power model with fiber optic triggering so I am not sure why the trigger batteries would effect the strobe power output but I will try new ones just to see.
I still am interested in picking up a "spare" if anyone has one available.
Was using mine in manual as well, when i had the issue, barely last week. My trigger takes two CR2450 batteries, and has two LEDs, so somehow assume one was getting the right charge, while the other was just emitting a weak light. Think Inon adjusts the light output based on a signal somehow. You can ask Pavel Kolpakov, he is a guru if it comes to strobe triggers.
Initially, one strobe was sometimes flashing sometimes not. After noticing red light on the trigger, I have then changed one (out of 2) batteries (in flash trigger) for a new one (only had one with me...), and it was working fine. After a few dives the older battery (2nd one) got a bit exhausted as well, with trigger flashing red again. Strobe, while it was still working, was emitting visibly weaker light, despite being on manual and the same settings as the other one. After i've exchanged the older battery as well, for a one salvaged from a spare Suunto, issue went away immediately.